Lighting technology has helped to trigger unprecedented energy consumption and the inevitable development of a power infrastructure to support a growing range of services. Rising demand and the cost of energy has led lighting providers to constantly seek new ways of achieving greater energy efficiency. As a result, the market has become a patchwork quilt of lighting technologies, serving a shifting assortment of applications. An examination of each technology’s design, operating principles, strengths and weaknesses, and applications offers a glimpse of the role it may play in the future.
Perhaps the most common form of lighting until recently, incandescent bulbs produce light by passing electric current through a thin filament, which becomes white-hot, emitting light over 360 degrees. Because of the light’s omnidirectional emission, the bulb must have reflectors to focus a large portion of the light on the desired area. Although the incandescent bulb’s lifespan is short—roughly 1,200 hours—the bulbs maintain their luminescence well throughout their operating life.
Incandescent bulbs provide a range of color temperatures, but the three primary options for consumers include soft white (measured at 2,700–3,000 degrees Kelvin), cool white (3,500 K–4,100 K) and daylight (5,000 K–6,500 K). Incandescent lights turn on almost instantly, and they are sensitive to voltage inputs, dimming as voltage is reduced. Incandescent dimming, however, greatly affects power consumption, operating life and color temperature.
The technology’s Achilles heel lies in its efficiency. An incandescent light bulb wastes 95% of the energy it generates, consuming four times more energy than a fluorescent alternative and six times more than LED bulbs. Incandescent source efficiency—the amount of light emitted from the bulb—measures about 10 lumens per watt, and its system efficiency—the amount of light that reaches the target area—is even lower. This inefficiency has led many parts of the world to pass legislation phasing out this type of lighting.
The technology’s slide toward extinction, however, may be reversed by recent design improvements that promise to make the incandescent bulb more efficient. Researchers at MIT have created a secondary structure around the incandescent filament made from a specially developed photonic crystal. The structure captures infrared energy and allows visible light to pass through. The scientists contend that the new design achieves an efficiency of 6.6 %—three times the efficiency of a standard bulb—and they think the bulb’s efficiency could be increased to 40%, which would surpass the performance of both LEDs and compact fluorescent lights (CFLs).
Closest in design to the incandescent light bulb, halogen lamps consist of tungsten filaments, enclosed in a quartz envelope filled with high-pressure halogen gases, such as iodine and bromine. These gases enable the lamp’s filament to heat to higher temperatures than incandescent bulbs. This causes the tungsten atoms to evaporate and combine with the halogen gas, triggering a chemical reaction that redeposits evaporated tungsten back onto the filament, increasing its life and maintaining the clarity of the envelope. This produces 12–22 lumens per watt and higher color temperature than incandescent lamps, with a lifespan of 1,000 hours.
However this technology has a number of shortcomings that must be considered when included in a design. Because the heat is concentrated on a smaller envelope surface and the surface is closer to the filament, halogen lamps get hotter than incandescent bulbs. The high temperature is essential to their operation, but it can pose burn and fire hazards. While halogen lamps offer slightly greater luminous efficacy than traditional incandescent lamps, their performance is still low compared with alternatives like fluorescent and LED lighting.
On the plus side, halogen lamps do not contain any mercury, and manufacturers like General Electric (GE) claim the lamps do not contain any materials that can be classified as hazardous waste. Also, the small size of halogen lamps permits designers to use the technology in compact optical systems for projectors and illumination. Perhaps the greatest advantage of halogen bulbs is the quality of lighting they provide. “Halogen produces very beautiful, sparkling light, with perfect color rendering,” says David Vanbeselaere, marketing manager for Philips Lighting.
Consequently halogen lamps are used in a variety of applications, including home and retail lighting, as well as automobile headlights. But even in these applications, halogen lighting’s days are numbered. “Halogen lighting still performs best in applications that require high light output from a small source,” says Todd Peterson, director of engineering at Revolution Lighting Technologies. “This will continue for the next five years until small-package LED technology improves to the point where the light output will match that of a halogen bulb.”
A high-efficiency light source, fluorescent lamps provide excellent illumination for areas where lighting is left on for prolonged periods of time, and for applications that do not require full brightness. Raising the bar for performance and energy efficiency, these lamps generate less heat than incandescent bulbs and convert electricity to light more efficiently, with luminous efficacy of 40–70 lumens per watt and life spans of 6,000–15,000 hours. Cost also works in favor of the technology. Fluorescent lighting offers consumers a nice balance between up-front cost and payback derived from energy savings.
To generate light, fluorescent bulbs pass electric current between tungsten electrodes on opposite sides of the lamp through low-pressure mercury vapor to produce ultraviolet (UV) energy. This energy excites phosphor materials coating the inside of the bulb, creating visible light.
Unlike many other light sources, fluorescent lights cannot receive electricity directly. Instead, they require ballasts to regulate the flow of current. The ballast provides the starting voltage and limits the current that passes through the lamp.
Intended to replace incandescent light bulbs, a variant design—CFLs—uses a curved or folded tube to fit into the space typically allotted for incandescent bulbs. Advances in phosphor formulations have improved the perceived color of the light emitted by CFLs. In fact, some sources see CFLs "soft white" as similar in color to standard incandescent lamps.
Despite all of these advantages, the light source suffers from significant disadvantages. All fluorescent lamps contain toxic mercury, which makes their disposal difficult. Also, the lamps take time to achieve full brightness, and their diffused light falls short when a focused beam is required. In addition, fluorescent lights are sensitive to ambient temperature. As a result, their light output can decline in cold conditions.
Poorly designed ballasts also cause a number of problems. Fluorescent flicker can be irritating to users, and inferior ballasts can create radio interference that disturbs nearby electronics or cause fires if they overheat.
While fluorescent lamps provide excellent value for the money, their long-term prospects are not good. “At this point, we see that LED technology has surpassed fluorescent in energy savings and lifetime, and well-designed LED bulbs provide better light quality as well,” says Vanbeselaere.
Light-emitting diodes, or LEDs, offer the highest luminous efficacy and lifespan of all residential and commercial lighting options. While they often come with the highest price tag, LEDs consume 75% less energy than incandescent bulbs and 40% less than fluorescent lighting. LEDs also outlive competing technologies, lasting 25 times longer than incandescent and halogen bulbs, and three times longer than most CFLs. In addition to energy efficiency, this lighting technology generates little heat and boasts robust construction, owing to the fact that it has no filament that can break.
Unlike other lighting options, LEDs are the offspring of the silicon revolution. Essentially LEDs are simply tiny light bulbs integrated into an electrical circuit that create light when electrons move through semiconductor material.
A two-lead semiconductor light source, an LED is a p–n junction diode, emitting light when activated by the flow of electrical current. When a voltage is applied to the leads, electrons recombine with electron holes within the device, releasing energy in the form of light (an effect called electroluminescence). The energy band gap of the semiconductor determines the color of the light, and LED manufacturers use integrated optical components to shape the bulb’s radiation pattern.
Often LEDs have a small footprint (some as little as 1 mm2). This makes the light source an attractive option for designers confronted with space constraints.
All in all, LEDs offer features that complement a wide variety of applications and enable a range of new features. “LEDs will become the new normal,” says Vanbeselaere. “While most recognized for superior energy efficiency and extended lifetime, advancements in LED technology have also improved light quality and design aesthetics.”
Raising the IQ Quotient of Lighting Systems
While LED lamps set the bar for energy efficiency, developers of lighting technology saved the best for last with the introduction of “smart lighting.” While this term means different things to different people, common elements of all definitions include unprecedented levels of energy efficiency and convenience. This metamorphosis has been enabled by the addition of sensing and communications capabilities to lighting systems, introducing degrees of control and interactivity that traditional technology just cannot match.
Harnessing heat and motion sensors, smart lighting can decide when illumination is required, based on room occupancy. Light sensors can use natural lighting as a criterion for reducing man-made lighting. By leveraging multiple sensor streams, smart technology goes one step further, enabling bulbs and switches to determine when, where and how much illumination is required. This level of visibility and control opens the door for automated energy management that can make a real difference. Simply dimming a lamp 5% to 10% can positively affect power usage and help to prevent energy waste.
A number of smart LEDs also include wireless communications, such as Wi-Fi, Z-Wave and Zigbee. With this connectivity, consumers can control and adjust lighting remotely, using a smartphone or tablet.
The Lighting Revolution
All these advances in lighting promise to revolutionize the way we live and work. They will add an extra measure of convenience, reduce energy consumption, and even transform the basic light bulb into a design element. As impressive as these changes are, they are only just beginning.
“Smart lighting will play a big role—we are at early adoption stage in the smart home space, but the smart home space is expected to grow by threefold by 2020,” says Kathy Sterio, general manager of Consumer Product Management and Marketing at GE Lighting.